Method for metal concentration, method for metal recovery, device for metal concentration, and device for metal recovery

ABSTRACT

An objective of invention is conveniently concentrating a metal in a metal ion-containing solution with high efficiency and to recover the metal from the metal ion-containing solution with high recovery efficiency. A method for concentrating or recovering a metal in a metal ion-containing solution in the present invention is the method comprising the following steps, a reduction and accumulation step to reduce the metal ion into a metal fine particle and also to accumulate the metal fine particle in the microorganism by allowing the microorganism and an electron donor B to act on a metal ion-containing solution W 0  and thus to obtain a solution W 1  that contains a microorganism having a metal fine particle accumulated therein; a concentration step to concentrate the solution W 1  that contains the microorganism having a metal fine particle accumulated therein by a filtration membrane and thus to obtain a concentrated solution W 2 ; and a return step to return the concentrated solution W 2  to first step above and thus to circulate. Further, A device for metal concentration or recovering in the present invention comprises the following: a storage unit  2  to store the solution W 1 , a concentration unit  3  to concentrate the solution W 1  that is transferred from the storage unit  2  by a filtration membrane, and a return unit  4  to return a concentrated solution W 2  that is concentrated in the concentration unit  3  to the storage unit  2.

TECHNICAL FIELD

The present invention relates to a method for metal concentration, amethod for metal recovery, a device for metal concentration, and adevice for metal recovery.

This application is based upon and claims the benefit of priority of theprior Japanese Patent Application No. 2013-008537, filed on Jan. 21,2013, the entire contents of which are incorporated herein by reference.

BACKGROUND ART

It has been widely performed to recover a metal from a solutioncontaining a metal such as industrial waste water or pregnant leachliquor for the purpose of reuse of resources other than the purpose tomeet the water quality standards of the legal regulation. However, metalrecovery from a metal ion-containing solution by a general techniquerequires high energy consumption and thus environmental impact is great.In particular, metal recovery from a metal ion-containing solutioncontaining a metal to be the target of recovery at a low concentrationis not substantially performed for economic reasons. To cope with theseproblems, there is an efficient method to recover a metal from a metalion-containing solution using a microorganism. As the method to recovera metal from a metal ion-containing solution using a microorganism, forexample, there are the following methods (i) to (iii).

(i) A method in which iron-reducing bacteria such as Shewanella algaeare allowed to act on a metal ion-containing solution so as to reduce ametal ion into a metal fine particle by the iron-reducing bacteria andalso to accumulate the metal fine particle in the iron-reducing bacteriaor to directly adsorb a metal ion on the iron-reducing bacteria, and theiron-reducing bacteria having the metal fine particle accumulatedtherein or the metal ion adsorbed thereon are recovered, therebyrecovering a metal (for example, Patent Documents 1 and 2).

(ii) A method in which iron-oxidizing bacteria are allowed to act on asolution containing ferrous ion so as to oxidize the ferrous ion intoferric ion, the pH of the solution is controlled so as to form iron(III)hydroxide, and the solid-liquid separation is conducted, therebyrecovering iron (Patent Document 3).

(iii) A method in which bacteria of the genus Shewanella are added to acolloidal silica solution containing metal impurities such as Cu, Zn, Niand Mg, only the metal impurities are accumulated in the bacteria of thegenus Shewanella, and the bacteria of the genus Shewanella having themetal incorporated therein is recovered, thereby separating theimpurities from colloidal silica (Patent Document 4).

In the method (i), it is required to increase the contact efficiencybetween the metal ion and the microorganism by introducing a greatamount of microorganism to act on the metal ion in order to increase therecovery efficiency, but the cost increases when a great amount ofmicroorganism is used. Hence, it is difficult to continuously recoverthe metal from the metal ion-containing solution with high recoveryefficiency at low cost. It is required a method capable of increasingthe concentration of the microorganism at the time of accumulating themetal fine particle or adsorbing the metal ion in order to increase therecovery efficiency especially in a case in which the metal ioncontained in water at a low concentration is reduced into a metal fineparticle by the microorganism and also the metal fine particle isaccumulated in the iron-reducing bacteria or the metal ion is directlyadsorbed on the iron-reducing bacteria. In addition, in the method (ii),the pH control of the solution is complicated and thus the operation isintricate.

In the method (iii), there are a step of binding the microorganism withthe metal which takes one or more days, a step of adding a biocide, anda step of controlling the pH by the addition of an alkali, and thus thesteps are intricate and take a long period of time. In addition, in therecovery operation as well, strong stirring is required even afterobtaining a flock containing bacteria of the genus Shewanella and therecovery percentage of the metal is not that high (in particular, seeExamples of Patent Document 4).

CITATION LIST Patent Document

Patent Document 1: JP 2007-113116 A

Patent Document 2: JP 2010-162442 A

Patent Document 3: JP 2005-238181 A

Patent Document 4: JP 2005-298276 A

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

As a method to recover a metal from a solution containing a useful metalresource in industry, various methods have been investigated asdescribed above, but these methods have a problem that the recoveryefficiency is low and the steps are intricate and thus an increase incost is caused in order to increase the recovery efficiency. The aim ofthe invention is to solve such a problem of the related art.

Means for Solving Problem

The invention provides a method for metal concentration, a method formetal recovery, a device for metal concentration and a device for metalrecovery which are able to conveniently concentrate a metal in a metalion-containing solution with high efficiency and to recover the metalfrom the metal ion-containing solution with high recovery efficiency.

In other words, the invention has the following aspects.

[1] A method for concentrating a metal in a metal ion-containingsolution, the method including the following steps (1) to (3):

(1) a reduction and accumulation step to reduce the metal ion into ametal fine particle and also to accumulate the metal fine particle in amicroorganism by allowing the microorganism and an electron donor to acton a metal ion-containing solution and thus to obtain a solution thatcontains the microorganism having a metal fine particle accumulatedtherein;

(2) a concentration step to concentrate the solution that contains themicroorganism having a metal fine particle accumulated therein by afiltration membrane and thus to obtain a concentrated solution; and

(3) a return step to return the concentrated solution to step (1) aboveand thus to circulate.

[2] The method for metal concentration according to [1], in which themetal ion is ions of one or more elements selected from the groupconsisting of Au, Ag, Pt, Pd, Rh, Ir, Ru and Os.

[3] The method for metal concentration according to [1] or [2], in whicha metal that is produced by reducing the metal ion coexists when amicroorganism and an electron donor act on a metal ion-containingsolution in step (1) above.

[4] The method for metal concentration according to any one of [1] to[3], in which the electron donor is an organic substance having from 1to 7 carbon atoms.

[5] The method for metal concentration according to any one of [1] to[4], in which the electron donor is at least one or both of an aliphaticcarboxylic acid having from 1 to 3 carbon atoms and a salt thereof.

[6] The method for metal concentration according to any one of [1] to[5], in which the electron donor is at least one or both of formic acidand a salt thereof.

[7] The method for metal concentration according to any one of [1] to[6], in which the microorganism is iron-reducing bacteria.

[8] The method for metal concentration according to [7], in which theiron-reducing bacteria are bacteria belonging to the genus Shewanella.

[9] The method for metal concentration according to [8], in which thebacteria belonging to the genus Shewanella are Shewanella algae orShewanella oneidensis.

[10] The method for metal concentration according to any one of [1] to[9], in which an average pore size of the filtration membrane is from0.01 to 1.0 μm.

[11] A method for metal recovery, the method for recovering themicroorganism that is obtained in the method for metal concentrationaccording to any one of [1] to [10] and has a metal fine particleaccumulated therein, the method further including the following step(4):

(4) a recovery step to recover the solution that contains themicroorganism having a metal fine particle accumulated therein so as tohave a cell concentration of 1.0×10¹⁷ cells/m³ or less.

[12] A method for recovering a metal from a metal ion-containingsolution, the method including the following steps (1′) to (4′):

(1′) an accumulation step to accumulate a metal ion in a microorganismby allowing a microorganism to act on a metal ion-containing solutionand thus to obtain a solution that contains the microorganism having ametal ion accumulated therein;

(2′) a concentration step to concentrate the solution that contains themicroorganism having a metal ion accumulated therein by a filtrationmembrane and thus to obtain a concentrated solution;

(3′) a return step to return the concentrated solution to step (1′)above and thus to circulate; and (4′) a recovery step to recover thesolution that contains the microorganism having a metal fine particleaccumulated therein so as to have a cell concentration of 1.0×10¹⁷cells/m³ or less.

[13] The method for metal recovery according to [12], in which the metalion is ions of one or more elements selected from the group consistingof Ga, In, Zn, Sn and a lanthanoid.

[14] The method for metal recovery according to [12] or [13], in whichthe microorganism is iron-reducing bacteria.

[15] The method for metal recovery according to [14], in which theiron-reducing bacteria are bacteria belonging to the genus Shewanella.

[16] The method for metal recovery according to [15], in which thebacteria belonging to the genus Shewanella are Shewanella algae orShewanella oneidensis.

[17] The method for metal recovery according to any one of [12] to [16],in which an average pore size of the filtration membrane is from 0.01 to1.0 μm.

[18] A device for metal concentration, including the following (a) to(c):

(a) a storage unit to store a solution that is obtained by allowing amicroorganism and an electron donor to act on a metal ion-containingsolution so as to reduce a metal ion into a metal fine particle and alsoto accumulate the metal fine particle in the microorganism or byallowing the microorganism to act on a metal ion-containing solution soas to accumulate a metal ion in the microorganism and contains amicroorganism having a metal fine particle or a metal ion accumulatedtherein;

(b) a concentration unit to concentrate the solution that is transferredfrom the storage unit and contains the microorganism having a metal fineparticle or a metal ion accumulated therein by a filtration membrane;and

(c) a return unit to return a concentrated solution that is concentratedin the concentration unit to the storage unit.

[19] The device for metal concentration according to [18], the devicefurther including the following (e):

(e) a measurement unit to measure a cell concentration of the solutionthat is supplied to the concentration unit and contains themicroorganism having a metal fine particle or a metal ion accumulatedtherein.

[20] A device for metal recovery, the device including the above (a) to(c) and the following (d):

(d) a recovery unit to recover the solution that contains themicroorganism having a metal fine particle or a metal ion accumulatedtherein from at least one or both of the storage unit and theconcentration unit.

[21] The device for metal recovery according to [20], the device furtherincluding the following (e):

(e) a measurement unit to measure a cell concentration of the solutionthat is supplied to the concentration unit and contains themicroorganism having a metal fine particle or a metal ion accumulatedtherein.

In addition, the invention has the following aspects.

<1> A metal recovery method to recover a specific metal from a solutioncontaining a metal ion, in which:

a microorganism is allowed to act on the solution containing a metal ionso as to reduce the metal ion into a metal fine particle by themicroorganism and also to accumulate the metal fine particle in themicroorganism,

a solution that contains the microorganism having the metal fineparticle accumulated therein is transferred to a concentration unit andconcentrated by filtering through a filtration membrane, and

a concentrated solution that contains the microorganism having the metalfine particle accumulated therein is continuously recovered.

<2> A metal recovery method to recover a specific metal from a solutioncontaining a metal ion, in which:

a microorganism is allowed to act on the solution containing a metal ionso as to directly adsorb the metal ion on the microorganism,

a solution that contains the microorganism having the metal ion adsorbedthereon is transferred to a concentration unit and concentrated byfiltering through a filtration membrane, and

a concentrated solution that contains the microorganism having the metalion adsorbed thereon is continuously recovered.

<3> The method for metal recovery according to <1> or <2>, in which themicroorganism is iron-reducing bacteria.

<4> The method for metal recovery according to <3>, in which theiron-reducing bacteria are bacteria belonging to the genus Shewanella.

<5> The method for metal recovery according to <4>, in which thebacteria belonging to the genus Shewanella are Shewanella algae orShewanella oneidensis.

<6> The method for metal recovery according to <1>, in which the metalion is ions of one or more elements selected from the group consistingof Au, Ag, Pt, Pd, Rh, Ir, Ru and Os.

<7> The method for metal recovery according to <2>, in which the metalion is ions of one or more elements selected from the group consistingof Ga, In, Zn, Sn and a lanthanoid.

<8> A device for metal recovery, including:

a concentration unit to which a solution that contains a microorganismobtained by allowing a microorganism to act on a solution containing ametal ion so as to reduce the metal ion into a metal fine particle bythe microorganism and also to accumulate the metal fine particle or amicroorganism having the metal ion adsorbed thereon is transferred andin which the microorganism having the metal fine particle accumulatedtherein or the metal ion adsorbed thereon in the solution isconcentrated by a filtration membrane and

a recovery unit in which a concentrated solution obtained byconcentrating the microorganism having the metal fine particleaccumulated therein or the metal ion adsorbed thereon is continuouslyrecovered from the concentration unit.

<9> The device for metal recovery according to <8>, the device furtherincludes:

a reaction tank in which a microorganism is allowed to act on a solutioncontaining a metal ion.

<10> The device for metal recovery according to <8> or <9>, in which thefiltration membrane is installed on the circulation line provided to aconcentration tank.

<11> The device for metal recovery according to <9> or <10>, in which atleast one of the reaction tank and the preceding stage of the reactiontank is provided with a gas removing means to remove oxygen in asolution.

Effect of the Invention

According to the method for metal concentration or the method for metalrecovery of the invention, it is possible to conveniently concentrate ametal in a metal ion-containing solution with high efficiency and thusto recover the metal with high recovery efficiency.

By means of the device for metal concentration or the device for metalrecovery according to the invention, it is possible to convenientlyconcentrate a metal in a metal ion-containing solution with highefficiency and thus to recover the metal with high recovery efficiency.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic block diagram illustrating an example of thedevice for metal recovery of the invention; and

FIG. 2 is a schematic block diagram illustrating an example of thedevice for metal recovery of the invention.

MODE(S) FOR CARRYING OUT THE INVENTION

<Device for Metal Concentration or Device for Metal Recovery>

The device for metal concentration of the invention has the following(a) to (c):

(a) a storage unit to store a solution that is obtained by allowing amicroorganism and an electron donor to act on a metal ion-containingsolution so as to reduce a metal ion into a metal fine particle and alsoto accumulate the metal fine particle in the microorganism or byallowing the microorganism to act on a metal ion-containing solution soas to accumulate a metal ion in the microorganism and contains amicroorganism having a metal fine particle or a metal ion accumulatedtherein;

(b) a concentration unit to concentrate the solution that is transferredfrom the storage unit and contains the microorganism having a metal fineparticle or a metal ion accumulated therein by a filtration membrane;and

(c) a return unit to return a concentrated solution that is concentratedin the concentration unit to the storage unit.

In addition, the device for metal recovery of the invention has thefollowing (d) in addition to (a) to (c) above:

(d) a recovery unit to recover the solution that contains themicroorganism having a metal fine particle or a metal ion accumulatedtherein from at least one or both of the storage unit and theconcentration unit.

In the invention, a device which does not include the recovery unit (d)is defined as a device for metal concentration and a device whichincludes the recovery unit (d) is defined as a device for metalrecovery. In other words, a device which includes a recovery unit totake out a solution containing a microorganism to the outside of thesystem is a device for metal recovery.

The device for metal concentration or device for metal recovery of theinvention may include one or both of the following (a₀) and (e):

(a₀) a supply unit to supply the metal ion-containing solution and themicroorganism or the metal ion-containing solution, the microorganismand the electron donor to the storage unit; and

(e) a measurement unit to measure a cell concentration of the solutionthat is supplied to the concentration unit and contains themicroorganism having a metal fine particle or a metal ion accumulatedtherein.

Hereinafter, the device for metal recovery of the invention will bedescribed with reference to an example thereof.

A device for metal recovery 1 of the present embodiment includes astorage unit 2, a concentration unit 3, a return unit 4, a recovery unit16, a measurement unit 5 and a supply unit 6.

In the device for metal recovery 1 of this example, the storage unit 2includes a reaction solution storage tank 10 and a stirring blade 10 a.The concentration unit 3 includes a membrane module 14 having afiltration membrane. The reaction solution storage tank 10 of thestorage unit 2 and the membrane module 14 of the concentration unit 3are connected to each other by a pipe 56. The return unit 4 includes apipe 58 of which one end is connected to the membrane module 14 and theother end is connected to the reaction solution storage tank 10. Thereaction solution storage tank 10 of the storage unit 2 and the recoveryunit 16 are connected to each other by a pipe 44. The supply unit 6includes a metal ion-containing solution storage tank 20, a bacterialculture storage tank 22 and an electron donor storage tank 24. Thereaction solution storage tank 10 of the storage unit 2 and the metalion-containing solution storage tank 20 are connected to each other by apipe 50. The reaction solution storage tank 10 of the storage unit 2 andthe bacterial culture storage tank 22 are connected to each other by apipe 52. The reaction solution storage tank 10 of the storage unit 2 andthe electron donor storage tank 24 are connected to each other by a pipe54.

In addition, the device for metal recovery 1 of this example includes afiltered water storage tank 18, and the membrane module 14 and thefiltered water storage tank 18 are connected to each other by a pipe 46to which a filtration pump 48 is provided in the middle.

[(a) Storage Unit]

To the reaction solution storage tank 10 of the storage unit 2, a metalion-containing solution W₀ is supplied from the metal ion-containingsolution storage tank 20 through the pipe 50 and a bacterial culture A₀is supplied from the bacterial culture storage tank 22 through the pipe52. An electron donor B is supplied from the electron donor storage tank24 through the pipe 54 in a case in which a metal ion is reduced into ametal fine particle and also the metal fine particle is accumulated in amicroorganism.

In the reaction solution storage tank 10, the metal ion-containingsolution W₀, the bacterial culture A₀, and the electron donor B whichhave been supplied are stirred and mixed with the stirring blade 10 a. Ametal ion in the metal ion-containing solution W₀ is reduced to producea metal fine particle and also the metal fine particle is accumulated ina microorganism in a case in which the electron donor B is suppliedtogether with the metal ion-containing solution W₀ and the bacterialculture A₀. A metal ion in the metal ion-containing solution W₀ isaccumulated by being directly adsorbed on a microorganism in a case inwhich the electron donor B is not supplied. By virtue of this, asolution W₁ that contains a microorganism having a metal fine particleaccumulated therein (hereinafter, referred to as the metal fine particleaccumulated microorganism) or a microorganism having a metal ionaccumulated therein (hereinafter, referred to as the metal ionaccumulated microorganism) is obtained.

As the material of the reaction solution storage tank 10, a knownmaterial can be adopted as long as it is hardly corroded by the metalion-containing solution W₀, the bacterial culture A₀, and the electrondonor B and does not adversely affect the action of the microorganismand the electron donor.

[(b) Concentration Unit]

To the membrane module 14 in the concentration unit 3, the solution W₁containing the metal fine particle accumulated microorganism or themetal ion accumulated microorganism is supplied from the reactionsolution storage tank 10 through the pipe 56.

A secondary side (filtered water side) 14 b of the filtration membranein the membrane module 14 is connected to the filtration pump 48 throughthe pipe 46. A concentrated solution W₂ containing the metal fineparticle accumulated microorganism or the metal ion accumulatedmicroorganism is obtained from a primary side 14 a of the filtrationmembrane and a filtered water W₃ is obtained from the secondary side 14b as the filtration pump 48 works.

The filtration membrane is not particularly limited as long as amembrane can capture the metal fine particle accumulated microorganismor the metal ion accumulated microorganism, and it is possible to use aknown membrane such as a hollow fiber membrane, a flat membrane, atubular membrane and a monolithic film. Among them, a hollow fibermembrane is preferable as the filtration membrane since it has a highvolume packing factor.

The material of the filtration membrane is not particularly limited aslong as a material is not corroded by the solution W₁ containing themetal fine particle accumulated microorganism or the metal ionaccumulated microorganism, and it is possible to use an inorganicmaterial such as ceramics and an organic material such as cellulose, acellulose mixed ester, a polyolefin, a polysulfone, polyvinylidenefluoride (PVDF) and polytetrafluoroethylene (PTFE). Among them,ceramics, polyvinylidene fluoride (PVDF) and polytetrafluoroethylene(PTFE) are preferable as the material of the filtration membrane fromthe viewpoint of being strong against a chemical or a pH change.

The average pore size of the micropores formed on the filtrationmembrane is not particularly limited as long as the metal fine particleaccumulated microorganism or the metal ion accumulated microorganism canbe captured, and it is preferably from 0.01 to 1.0 μm and morepreferably from 0.05 to 0.4 μm.

It is easy to decrease the pressure required for membrane filtration andto increase the concentration efficiency of the metal fine particle orthe metal ion when the average pore size of the micropores is equal toor greater than the lower limit value. In addition, it is easy tosuppress the leakage of the metal fine particle accumulatedmicroorganism or the metal ion accumulated microorganism to thesecondary side of the filtration membrane when the average pore size ofthe micropores is equal to or less than the upper limit value.

The effective membrane area of the membrane module 14 is notparticularly limited, and it may be a membrane area in which a desiredamount of the filtered water W₃ is obtained by the filtration pump 48.The effective membrane area of the membrane module 14 is preferably setto a membrane area so as to have a filtration linear velocity (LV) offrom 0.1 to 1 m/day when obtaining a desired amount of the filteredwater W₃ by the filtration pump 48 from the viewpoint of favorablefiltration efficiency and prevention of membrane clogging.

[(c) Return Unit]

In the return unit 4, the concentrated solution W₂ obtained from theprimary side 14 a of the filtration membrane in the membrane module 14is returned to the reaction solution storage tank 10 through the pipe 58and circulated. By virtue of this, the cell concentration of thesolution W₁ containing the metal fine particle accumulated microorganismor the metal ion accumulated microorganism in the reaction solutionstorage tank 10 increases. In addition, it is possible to enhance theconcentration efficiency since the microorganism in the concentratedsolution W₂ which has been returned is reusable in the reaction solutionstorage tank 10 unless otherwise the metal fine particle accumulatedmicroorganism or the metal ion accumulated microorganism loses theability to accumulate the metal fine particle or to adsorb the metalion.

[(a₀) Supply Unit]

The device for metal recovery 1 of this example includes the supply unit6 including the metal ion-containing solution storage tank 20, thebacterial culture storage tank 22 and the electron donor storage tank24.

The metal ion-containing solution storage tank 20 is a storage tank totemporarily store the metal ion-containing solution W₀. The metalion-containing solution storage tank 20 is not particularly limited aslong as a storage tank can store the metal ion-containing solution W₀.

The bacterial culture storage tank 22 is a storage tank to temporarilystore the bacterial culture A₀. The bacterial culture storage tank 22 isnot particularly limited as long as a storage tank can store thebacterial culture A₀.

The electron donor storage tank 24 is a storage tank to temporarilystore the electron donor B which is required when the metal ioncontained in the metal ion-containing solution W₀ is reduced into themetal fine particle by the action of the microorganism. The electrondonor storage tank 24 is not particularly limited as long as a storagetank can store the electron donor B.

[(d) Recovery Unit]

The device for metal recovery 1 of this example includes the recoveryunit 16 to recover the solution W₁ containing the metal fine particleaccumulated microorganism or the metal ion accumulated microorganismwhich is sent from the reaction solution storage tank 10 through thepipe 44.

The recovery unit 16 is not particularly limited as long as a recoveryunit can recover the solution W₁ containing the metal fine particleaccumulated microorganism or the metal ion accumulated microorganism.

In addition, the device for metal recovery 1 may be a device in whichthe solution W₁ flows to the recovery unit 16 and the solution W₁ isrecovered as the valve and pump provided to the passage (for example,pipe 44) from the reaction solution storage tank 10 to the recovery unit16 work when the measurement unit 5 to be subsequently described detectsthat the cell concentration is equal to or greater than a predeterminedvalue.

[(e) Measurement Unit]

The device for metal recovery 1 of this example includes the measurementunit 5 to measure the cell concentration of the solution W₁ containingthe metal fine particle accumulated microorganism or the metal ionaccumulated microorganism to be supplied from the reaction solutionstorage tank 10 of the storage unit 2 to the concentration unit 3.

The measurement unit 5 of this example is installed outside the reactionsolution storage tank 10 and measures the cell concentration of thesolution W₁ containing the metal fine particle accumulated microorganismor the metal ion accumulated microorganism sampled from the reactionsolution storage tank 10. Incidentally, the measurement unit 5 may bedesigned so as to directly measure the cell concentration of thesolution W₁ containing the microorganism having a metal fine particle ora metal ion accumulated therein inside the reaction solution storagetank 10 or inside the pipe 56.

The measurement unit 5 is not particularly limited as long as ameasurement unit can measure the cell concentration of the solution W₁containing the microorganism having a metal fine particle or a metal ionaccumulated therein.

[Filtered Water Storage Tank]

The device for metal recovery 1 of this example includes the filteredwater storage tank 18 to store the filtered water W₃ that has passedthrough the filtration membrane of the membrane module 14. The filteredwater storage tank 18 is not particularly limited as long as a storagetank can store the filtered water W₃.

The filtered water storage tank 18 may include a pH adjusting means toadjust the pH of the filtered water W₃ to the range that is suitable fordischarge into a river, if necessary.

The pH adjusting means may be one which can adjust the pH of thefiltered water W₃ to a desired pH, and examples thereof may include a pHmeter and a means equipped with an acid addition apparatus and an alkaliaddition apparatus.

[Mechanism of Action]

In the device for metal recovery 1, the metal ion-containing solutionW₀, the bacterial culture A₀ and the electron donor B are supplied fromthe metal ion-containing solution storage tank 20, the bacterial culturestorage tank 22 and the electron donor storage tank 24 to the reactionsolution storage tank 10 of the storage unit 2, respectively, in a casein which a metal ion is reduced into a metal fine particle by amicroorganism and also the metal fine particle is accumulated in themicroorganism. The metal ion-containing solution W₀ and the bacterialculture A₀ are supplied from the metal ion-containing solution storagetank 20 and the bacterial culture storage tank 22 to the reactionsolution storage tank 10 of the storage unit 2, respectively, in a casein which a metal ion is directly adsorbed on and accumulated in amicroorganism.

In the reaction solution storage tank 10, the metal ion contained in themetal ion-containing solution W₀ is reduced into a metal fine particleby the microorganism and also the metal fine particle is accumulated inthe microorganism or the metal ion is directly adsorbed on andaccumulated in the microorganism in a reaction solution containing themetal ion-containing solution W₀, the bacterial culture A₀ and, ifnecessary, the electron donor B. By virtue of this, the solution W₁containing the metal fine particle accumulated microorganism or themetal ion accumulated microorganism is obtained.

A portion of the solution W₁ containing the metal fine particleaccumulated microorganism or the metal ion accumulated microorganism istransferred from the reaction solution storage tank 10 of the storageunit 2 to the concentration unit 3 and filtered through the filtrationmembrane included in the membrane module 14. The concentrated solutionW₂ in which the metal fine particle accumulated microorganism or themetal ion accumulated microorganism is concentrated is returned to thereaction solution storage tank 10 through the pipe 58 of the return unit4. By virtue of this, the cell concentration of the solution W₁containing the metal fine particle accumulated microorganism or themetal ion accumulated microorganism in the reaction solution storagetank 10 increases in this manner, and as a result, the concentration ofthe metal fine particle or metal ion increases.

The solution W₁ containing the metal fine particle accumulatedmicroorganism or the metal ion accumulated microorganism which has beenconcentrated to a desired cell concentration is recovered to therecovery unit 16.

The filtered water W₃ filtered through the filtration membrane isdischarged after being subjected to the pH adjustment in the filteredwater storage tank 18 if necessary.

Examples of the device for metal concentration of the invention mayinclude a device which has the same configuration as the device formetal recovery 1 except that the pipe 44 and the recovery unit 16 arenot included.

In the device for metal recovery or device for metal concentration ofthe invention described above, the cell concentration in the storageunit is increased as a portion of the solution containing the metal fineparticle accumulated microorganism obtained by reducing the metal ioncontained in the metal ion-containing solution into a metal fineparticle and also accumulating the metal fine particle or the metal ionaccumulated microorganism obtained by directly adsorbing andaccumulating the metal ion is transferred to and concentrated in theconcentration unit and the concentrated solution is returned to thestorage unit. Hence, the metal fine particle accumulated microorganismor the metal ion accumulated microorganism can be reused for theaccumulation of the metal ion while being concentrated, thus it ispossible to concentrate the metal in the metal ion-containing solutionwith high efficiency, and as a result, it is possible to recover themetal with high efficiency. In addition, the pH control is also easysince it is not required to convert the metal ion contained in the metalion-containing solution into a hydroxide in order to recover the metal,and thus the operation is convenient.

Incidentally, the device for metal concentration or the device for metalrecovery of the invention is not limited to the device for metalconcentration having the same configuration as the device for metalrecovery 1 or the device for metal recovery 1.

For example, the device for metal concentration or the device for metalrecovery of the invention may be a device in which the reaction toreduce a metal ion in a metal ion-containing solution into a metal fineparticle by a microorganism and also to accumulate the metal fineparticle in the microorganism or the reaction to directly adsorb andaccumulate a metal ion in a microorganism is conducted in the pipe(line) of the preceding stage of the reaction solution storage tank bymixing a metal ion-containing solution, an electron donor and amicroorganism or a device (device for metal recovery 1′) in which thereaction solution storage tank is separately provided as a reaction tankand a concentration tank as illustrated in FIG. 2. In addition, thedevice for metal concentration or the device for metal recovery of theinvention may be a device which does not include an electron donorstorage tank in the case of directly adsorbing and accumulating a metalion in a microorganism, namely, not conducting a reduction reaction ofthe metal ion.

For example, in the case of using the device for metal recovery 1′, inthe method for metal recovery using the device for metal recovery 1′,the metal ion-containing solution W₀, the bacterial culture A₀ and theelectron donor B are supplied to a reaction tank 10′ and themicroorganism contained in the bacterial culture A₀ is allowed to act onthe metal ion-containing solution W₀ so as to reduce the metal ion inthe metal ion-containing solution W₀ into a metal fine particle by themicroorganism and also to accumulate the metal fine particle in themicroorganism in the reaction tank 10′. In addition, the solution W₁that contains the microorganism having the metal fine particleaccumulated therein is transferred to the concentration tank 12 whileallowing the microorganism to act on the metal ion-containing solutionW₀.

Specifically, while stirring with a stirring blade 10 a, to the reactiontank 10′, the metal ion-containing solution W₀ is supplied from themetal ion-containing solution storage tank 20 through the pipe 50, thebacterial culture A₀ is supplied from the bacterial culture storage tank22 through the pipe 52 and the electron donor B is supplied from theelectron donor storage tank 24 depending on the metal species. Inaddition, a portion of the solution W₁ containing the microorganismhaving the metal ion accumulated therein is continuously withdrawn andtransferred to the concentration tank 12 through a pipe 42 whilereducing the metal ion in the metal ion-containing solution into a metalfine particle by the microorganism and also accumulating the metal fineparticle in the microorganism in the reaction tank 10′.

In addition, the device for metal concentration or the device for metalrecovery of the invention may be a device which does not include any oneor more of the measurement unit, the supply unit and the filtered waterstorage tank.

In addition, it may be a device which is equipped with a recovery unitto recover the solution containing the metal fine particle accumulatedmicroorganism or the solution containing the metal ion accumulatedmicroorganism from the concentration unit, or it may be a device whichis equipped with a recovery unit to recover the solution containing themetal fine particle accumulated microorganism or the solution containingthe metal ion accumulated microorganism from both of the storage unitand the concentration unit.

In addition, in a case in which the electron donor remains in thefiltered water, the device for metal concentration or the device formetal recovery of the invention may be a device which is provided, forexample, with a membrane that can concentrate the remaining electrondonor such as a reverse osmosis membrane and a return pipe to return anaqueous solution containing the concentrated electron donor to thereaction solution storage tank or the electron donor storage tank andthus by which the electron donor remaining in the filtered water isrecovered and utilized.

In addition, in a case in which it is required to remove oxygen in thereaction solution upon reducing the metal ion contained in the metalion-containing solution into the metal fine particle and alsoaccumulating the metal fine particle in the microorganism or adsorbingthe metal ion directly on the microorganism, the device for metalconcentration or the device for metal recovery of the invention may be adevice which includes a means to remove oxygen in at least either of thereaction solution storage tank or the preceding stage of the reactionsolution storage tank. Specifically, it may be a device for metalconcentration or a device for metal recovery in which, for example, anyone or more of the metal ion-containing solution storage tank, thebacterial culture storage tank, the electron donor storage tank and thereaction solution storage tank and the pipe to which the metalion-containing solution, the bacterial culture or the electron donor issupplied is equipped with a means to remove oxygen.

Examples of the oxygen removing means may include a deaerator and anitrogen aerator.

<Method for Metal Concentration or Method for Metal Recovery>

The method for metal concentration of the invention is a method toconcentrate a specific metal in a solution containing a metal ion. Themethod for metal concentration of the invention is divided into a methodto concentrate a metal by utilizing a reducing and accumulating actionof a microorganism and a method to concentrate a metal by utilizing theadsorbing action of a microorganism.

In addition, the method for metal recovery of the invention is a methodto concentrate and recover a specific metal in a solution containing ametal ion.

Hereinafter, as an example of the method for metal concentration ormethod for metal recovery of the invention, a method using the devicefor metal recovery 1 described above will be described.

First Embodiment Concentration Method by Reducing and AccumulatingAction of Microorganism

The method for metal concentration using the device for metal recovery 1of the present embodiment includes the following steps (1) to (3). Inaddition, the method for metal recovery includes the following step (4)in addition to the following steps (1) to (3).

In the invention, a method which does not include the following step (4)is defined as a method for metal concentration and a method whichincludes the following step (4) is defined as a method for metalrecovery. In other words, to accumulate a metal in a microorganism andto increase the liquid phase cell concentration through separation ofthe microorganism by a filtration membrane and return thereof isreferred to as the “concentration” and to take out a solution thatcontains the microorganism having the metal accumulated therein to theoutside of the system is referred to as the “recovery”.

(1) A reduction and accumulation step to reduce the metal ion into ametal fine particle and also to accumulate the metal fine particle in amicroorganism by allowing a microorganism and an electron donor to acton a metal ion-containing solution W₀ and thus to obtain a solution W₁containing a metal fine particle accumulated microorganism.

(2) A concentration step to concentrate the solution W₁ containing ametal fine particle accumulated microorganism by a filtration membraneand thus to obtain a concentrated solution W₂.

(3) A return step to return the concentrated solution W₂ to step (1)above and thus to circulate.

(4) A recovery step to recover the solution W₁ containing a metal fineparticle accumulated microorganism.

(Step (1))

The metal ion-containing solution W₀, the bacterial culture A₀ and theelectron donor B are supplied to the reaction solution storage tank 10,respectively, and a microorganism contained in the bacterial culture A₀and the electron donor B are allowed to act on the metal ion-containingsolution W₀ so as to reduce the metal ion in the metal ion-containingsolution W₀ into a metal fine particle by the microorganism and also toaccumulate the metal fine particle in the microorganism. Specifically,while stirring with the stirring blade 10 a, to the reaction solutionstorage tank 10, the metal ion-containing solution W₀ is supplied fromthe metal ion-containing solution storage tank 20 through the pipe 50,the bacterial culture A₀ is supplied from the bacterial culture storagetank 22 through the pipe 52 and the electron donor B is supplied fromthe electron donor storage tank 24 through the pipe 54. In a reactionsolution containing the metal ion-containing solution W₀, the bacterialculture A₀ and the electron donor B, the microorganism reduces the metalion into a metal fine particle and also accumulates the metal fineparticle therein and thus the solution W₁ containing the metal fineparticle accumulated microorganism is obtained.

The microorganism used in the present embodiment is preferablyiron-reducing bacteria.

The iron-reducing bacteria cause the oxidation-reduction reaction usingthe electron donor B and a metal ion as the electron acceptor in thecase of a metal such as Au, Pt and Pd. At this time, the iron-reducingbacteria reduce a metal ion contained in the metal ion-containingsolution into a metal fine particle and also accumulate the metal fineparticle in their cells. Hence, the use of iron-reducing bacteria makesit possible to concentrate a metal ion in the metal ion-containingsolution W₀ as a metal fine particle.

Hence, the present embodiment is especially suitable when concentratingions of one or more elements selected from the group consisting of Au,Ag, Pt, Pd, Rh, Ir, Ru and Os, the so-called precious metal as a metalfine particle.

Examples of the iron-reducing bacteria may include the followingbacteria.

The genus Shewanella such as Shewanella algae (culture collectioninstitute (ATCC): 51181 strain and the like), Shewanella oneidensis(ATCC: 700550 strain and the like).

The genus Geobacter such as Geobacter metallireducens (ATCC: 53774strain and the like).

The genus Desulfuromonas such as Desulfuromonas palmitatis (ATCC: 51701strain and the like).

The genus Desulfuromusa such as Desulfuromusa kysingii (DSM (DeutscheSammlung von Mikroorganismen und Zellkulturen): 7343 strain and thelike).

The genus Pelobacter such as Pelobacter venetianus (ATCC: 2394 strainand the like).

The genus Ferrimonas such as Ferrimonas balearica (DSM: 9799 strain andthe like).

The genus Aeromonas such as Aeromonas hydrophila (ATCC: 15467 strain andthe like).

The genus Sulfurospirillum such as Sulfurospirillum barnesii (ATCC:700032 strain and the like).

The genus Wolinella such as Wolinella succinogenes (ATCC: 29543 strainand the like).

The genus Desulfovibrio such as Desulfovibrio desulfuricans (ATCC: 29577strain and the like).

The genus Geothrix such as Geothrix fermentans (ATCC: 700665 strain andthe like).

The genus Deferribacter such as Deferribacter thermophiles (DSM: 14813strain and the like).

The genus Geovibrio such as Geovibrio ferrireducens (ATCC: 51996 strainand the like).

The genus Pyrobaculum such as Pyrobaculum islandicum (DSM: 4184 strainand the like).

The genus Thermotoga such as Thermotoga maritime (DSM: 3109 strain andthe like).

The genus Archaeoglobus such as Archaeoglobus fulgidus (ATCC: 49558strain and the like).

The genus Pyrococcus such as Pyrococcus furiosus (ATCC: 43587 strain andthe like).

The genus Pyrodictium such as Pyrodictium abyssi (DSM: 6158 strain andthe like).

These iron-reducing bacteria are anaerobic bacteria.

As the iron-reducing bacteria, bacteria belonging to the genusShewanella are more preferable and Shewanella algae and Shewanellaoneidensis are even more preferable from the viewpoint that theaccumulation efficiency of a precious metal or a platinum group metal ismore favorable.

The microorganism may be one kind or two or more kinds.

The electron donor B is a substance required in a case in which thereduction reaction of the metal ion by an enzyme and the like of themicroorganism and the like are accompanied in the case of reducing themetal ion into a metal fine particle by the microorganism and alsoaccumulating the metal fine particle in the microorganism. As theelectron donor B, an optimal one may be appropriately used according tothe kind of the microorganism.

Examples of the electron donor B may include an electron donor composedof an organic substance having from 1 to 7 carbon atoms and hydrogen gas(molecular hydrogen). Among them, an electron donor composed of anorganic substance having from 1 to 7 carbon atoms is preferable as theelectron donor B from the viewpoint of ease of handling and solubilityin water.

Examples of the electron donor composed of an organic substance havingfrom 1 to 7 carbon atoms may include the following ones.

An aliphatic carboxylic acid salt (fatty acid salt) such as a formicacid salt and an acetic acid salt; an aromatic carboxylic acid salt suchas a benzoic acid salt; an oxocarboxylic acid salt such as a pyruvicacid salt; and a carboxylic acid salt such as a lactic acid salt.

An alcohol such as ethanol.

An unsaturated aromatic substance such as toluene phenol.

As the electron donor composed of an organic substance having from 1 to7 carbon atoms, at least one or both of an aliphatic carboxylic acidhaving from 1 to 3 carbon atoms and a salt thereof is preferable and atleast one or both of formic acid and a salt thereof is more preferablefrom the viewpoint of solubility in water.

The electron donor B may be one kind or two or more kinds.

The ratio of the amounts of the metal ion-containing solution W₀, thebacterial culture A₀ and the electron donor B supplied to the reactionsolution storage tank 10 may be set such that the theoretical initialconcentrations thereof in the reaction solution (microorganism cellsuspension) in the reaction solution storage tank 10 become a suitablecondition in a case in which the metal ion is reduced into a metal fineparticle by the microorganism and also the metal fine particle isaccumulated in the microorganism. Incidentally, the theoretical initialconcentrations refers to the concentrations of the metal ion-containingsolution W₀, the bacterial culture A₀ and the electron donor B in thereaction solution in a case in which the reaction has not yet proceeded.

The theoretical initial concentration of the metal ion in the reactionsolution in the reaction solution storage tank 10 is preferably from0.01 to 10 mM and more preferably from 0.1 to 5 mM from the viewpointthat the efficiency to reduce the metal ion into a metal fine particleby the microorganism and also to accumulate the metal fine particle inthe microorganism is more favorable.

The theoretical initial concentration of the electron donor B in thereaction solution in the reaction solution storage tank 10 is preferablyfrom 0.2 to 200 mM and more preferably from 1 to 50 mM from theviewpoint that the efficiency to reduce the metal ion into a metal fineparticle by the microorganism and also to accumulate the metal fineparticle in the microorganism is more favorable.

The theoretical initial concentration of the bacterial culture in thereaction solution in the reaction solution storage tank 10 is preferablyfrom 5.0×10¹² to 5.0×10¹⁶ cells/m³ and more preferably from 5.0×10¹³ to1.0×10¹⁶ cells/m³ from the viewpoint that the efficiency to reduce themetal ion into a metal fine particle by the microorganism and also toaccumulate the metal fine particle in the microorganism is morefavorable.

In step (1), it is preferable that a metal that is formed by reducing ametal ion coexists when the microorganism and the electron donor act onthe metal ion-containing solution from the viewpoint of improving theefficiency of the reduction reaction of the metal ion. The metal is ametal that is obtained by allowing the microorganism and the electrondonor used in the present embodiment to act so as to reduce the metalion into a metal fine particle and also to accumulate the metal fineparticle in the microorganism. The metal to coexist is preferably ametal that is obtained by reducing the same metal ion as the metal ioncontained in the metal ion-containing solution used in step (1).

The time at which a metal produced by reducing a metal ion is allowed tocoexist is not particularly limited, and it is preferable that the metalis supplied and coexists before the metal ion-containing solution W₀ andthe electron donor B are supplied or immediately after the supplythereof is started from the viewpoint of further enhancing theefficiency of the reduction reaction.

The coexisting amount of a metal that is produced by reducing a metalion is not particularly limited and is preferably from 1 to 200% by masswith respect to the produced amount (100% by mass) of the metal obtainedby conducting a batch reaction in the reaction solution storage tank 10in advance.

The form of the metal to coexist is not particularly limited and ispreferably a metal fine particle having a particle size of from 0.01 μmto 1 mm since the efficiency of reduction reaction is improved as thesurface area is greater. In addition, it is preferable to use the metalfine particle accumulated microorganism obtained by reducing the metalion in the metal ion-containing solution into a metal fine particle bythe microorganism and also accumulating the metal fine particle in themicroorganism.

Step (1) may be performed by a batch reaction or by a semi-batchreaction.

In the case of performing step (1) by a semi-batch reaction, it ispreferable that the supply of the metal ion-containing solution W₀, thebacterial culture A₀ and the electron donor B to the reaction solutionstorage tank 10 is adjusted in the range in which the reaction solutionin the reaction solution storage tank 10 can be maintained in apredetermined amount in consideration of the amount of the solution W₁containing the metal fine particle accumulated microorganism which istransferred to the concentration unit 3. The supply of the metalion-containing solution W₀, the bacterial culture A₀ and the electrondonor B to the reaction solution storage tank 10 may be continuous orintermittent as long as the reaction solution in the reaction solutionstorage tank 10 can be maintained in a predetermined amount.

In the case of performing step (1) by a semi-batch reaction, the averagehydraulic retention time (HRT) of the reaction solution in the reactionsolution storage tank 10 is preferably from 1 to 120 minutes and morepreferably from 5 to 80 minutes. The concentration efficiency of themetal is more favorable when the HRT in the reaction solution storagetank 10 is equal to or longer than the lower limit value, and as aresult, the recovery efficiency of the metal is more favorable. Thetreatment efficiency of the metal ion-containing solution is morefavorable when the HRT in the reaction solution storage tank 10 is equalto or shorter than the upper limit value.

The HRT in the reaction solution storage tank 10 can be adjusted by thesupply rate of the metal ion-containing solution W₀ to the reactionsolution storage tank 10, the transfer rate of the solution W₁containing the metal fine particle accumulated microorganism from thereaction solution storage tank 10 to the concentration unit 3 and thewithdrawal rate of the filtered water W₃ from the membrane module 14.

(Step (2))

In step (2), a portion of the solution W₁ containing the metal fineparticle accumulated microorganism is transferred from the reactionsolution storage tank 10 to the membrane module 14 of the concentrationunit 3 and concentrated by the filtration membrane to obtain theconcentrated solution W₂.

Specifically, the solution W₁ containing the metal fine particleaccumulated microorganism which has been transferred from the reactionsolution storage tank 10 is filtered through the filtration membraneincluded in the membrane module 14 by allowing the filtration pump 48 towork so as to be separated into the concentrated solution W₂ and thefiltered water W₃.

The filtration linear velocity (LV) is preferably from 0.1 to 1 m/day.

The filtered water W₃ that has been filtered through the filtrationmembrane is recovered through the pipe 46, stored in the filtered waterstorage tank 18, and then discharged into a river and the like afteradjusting the pH thereof if necessary.

(Step (3)) In step (3), the concentrated solution W₂ obtained in step(2) is returned to the reaction solution storage tank 10 of step (1) tobe circulated. By virtue of this, the cell concentration of the solutionW₁ containing the metal fine particle accumulated microorganism in thereaction solution storage tank 10 increases.

(Step (4))

In the present embodiment, it is preferable to recover the solution W₁containing the metal fine particle accumulated microorganism of whichthe cell concentration is increased in the reaction solution storagetank 10 to the recovery unit 16 through the pipe 44.

The cell concentration of the solution W₁ containing the metal fineparticle accumulated microorganism which is recovered from the reactionsolution storage tank 10 is preferably from 1.0×10¹⁵ to 5.0×10¹⁷cells/m³ and more preferably from 5.0×10¹⁶ to 1.0×10¹⁷ cells/m³. Therecovery efficiency of the metal is more favorable when the cellconcentration is equal to or greater than the lower limit value. It iseasy to continuously favorably maintain the solid-liquid separation bymembrane separation as well as the treatment efficiency of the metalion-containing solution is more favorable when the cell concentration isequal to or less than the upper limit value.

The time at which the solution W₁ containing the metal fine particleaccumulated microorganism is recovered can be determined, for example,by measuring the cell concentration of the solution W₁ containing themetal fine particle accumulated microorganism in the reaction solutionstorage tank 10 by the measurement unit 5.

The application of the metal obtained by the method for metalconcentration or method for metal recovery of the present embodiment isnot particularly limited. In the present embodiment, the metal fineparticle is in a state of being accumulated in the microorganism andthus can be used as a catalyst as it is. In addition, for example, themetal fine particle accumulated microorganism is baked in an electricfurnace or the like so as to remove the microorganism and impurities,and then the metal fine particle thus recovered or a separately preparedmetal mass (with high purity) may be used.

In the method for metal concentration or method for metal recoveryaccording to the first embodiment of the invention described above, aportion of the solution W₁ containing the metal fine particleaccumulated microorganism which is obtained in step (1) is concentratedby membrane filtration to obtain the concentrated solution W₂ in step(2) and the concentrated solution W₂ is returned to step (1) to becirculated in step (3), and thus the concentration of the metal fineparticle accumulated microorganism of the solution W₁ containing themetal fine particle accumulated microorganism increases. By virtue ofthis, it is possible to concentrate the metal in the metalion-containing solution with high efficiency and thus it is possible torecover the metal with high efficiency. In addition, the pH control isalso easy since it is not required to convert the metal ion contained inthe metal ion-containing solution into a hydroxide when recovering themetal, and thus the operation is convenient.

In addition, the method for metal concentration or method for metalrecovery of the first embodiment of the invention is not limited to themethod using the device for metal recovery 1 described above.

For example, it may be a method in which the reaction to reduce a metalion in a metal ion-containing solution into a metal fine particle by amicroorganism and also to accumulate the metal fine particle in themicroorganism is conducted in the pipe of the preceding stage of thereaction solution storage tank by mixing a metal ion-containingsolution, an electron donor and a microorganism.

In addition, it may be a method using a device (device for metalrecovery 1′) in which the reaction solution storage tank is separatelyprovided as a reaction tank and a concentration tank as illustrated inFIG. 2, for example.

In addition, in a case in which the electron donor remains in thefiltered water, it may be a method in which the remaining electron donoris concentrated, for example, using a membrane that can concentrate theelectron donor such as a reverse osmosis membrane, an aqueous solutioncontaining the concentrated electron donor is returned to the reactionsolution storage tank or the electron donor storage tank, and theremaining electron donor is recovered and utilized.

In addition, in a case in which it is required to remove oxygen in thereaction solution upon reducing the metal ion contained in the metalion-containing solution into a metal fine particle by the microorganismand also accumulating the metal fine particle in the microorganism, itmay be a method in which the removal of oxygen is conducted in at leasteither of the reaction solution storage tank or the preceding stage ofthe reaction solution storage tank.

Second Embodiment Concentration Method by Adsorbing Action Microorganism

In the above description, the embodiment using a reducing andaccumulating action of a microorganism on a metal fine particle isdescribed, but the invention can also be carried out using an adsorbingaction of a microorganism depending on the metal ionic species to be thetarget of concentration.

Hereinafter, an embodiment using an adsorbing action of a microorganismwill be described. However, in the second embodiment, the description onthe part which is common to the first embodiment will be omitted and theconfiguration and the mechanism which are different from those of thefirst embodiment will be described.

The present embodiment is especially suitable when concentrating andrecovering ions of one or more elements selected from the groupconsisting of Ga, In, Zn, Sn and a lanthanoid.

The method for metal recovery using the device for metal recovery 1 ofthe present embodiment includes the following steps (1′) to (4′).

(1′) An accumulation step to accumulate a metal ion in a microorganismby allowing a microorganism to act on a metal ion-containing solution W₀and thus to obtain a solution W₁ containing a metal ion accumulatedmicroorganism.

(2′) A concentration step to concentrate the solution W₁ containing ametal ion accumulated microorganism by a filtration membrane and thus toobtain a concentrated solution W₂.

(3′) A return step to return the concentrated solution W₂ to step (1′)above and thus to circulate.

(4′) A recovery step to recover the solution W₁ containing a metal ionaccumulated microorganism so as to have a cell concentration of 1.0×10¹⁷cells/m³ or less.

(Step (1′))

The metal ion is directly, namely, without undergoing theoxidation-reduction reaction adsorbed on the cell surface or inside thecell wall of the microorganism as the microorganism is allowed to act onthe metal ion-containing solution W₀ that contains an ion of a metalsuch as Ga, In, Zn, Sn and a lanthanoid. Hence, the metal ion isadsorbed on and accumulated in the microorganism as a microorganismwhich can adsorb a metal ion is allowed to act on the metalion-containing solution W₀, and thus the solution W₁ containing a metalion accumulated microorganism is obtained.

The difference between the accumulation by the reducing and accumulatingaction of step (1) of the first embodiment and the accumulation by theadsorbing action of step (1′) of the second embodiment is whether themicroorganism is allowed to act in a state of being able to cause anoxidation-reduction reaction or not.

In step (1′), the metal ion-containing solution W₀ and the bacterialculture A₀ are supplied to the reaction solution storage tank 10, andthe microorganism contained in the bacterial culture A₀ is allowed toact on the metal ion-containing solution W₀ so as to adsorb the metalion in the metal ion-containing solution W₀ on the microorganism in thereaction solution storage tank 10.

Specifically, while stirring with the stirring blade 10 a, to thereaction solution storage tank 10, the metal ion-containing solution W₀is supplied from the metal ion-containing solution storage tank 20through the pipe 50 and the bacterial culture A₀ is supplied from thebacterial culture storage tank 22 through the pipe 52. In the reactionsolution storage tank 10, the metal ion is adsorbed on and accumulatedin the microorganism in the reaction solution containing the metalion-containing solution W₀ and the bacterial culture A₀ and thus thesolution W₁ containing the metal ion accumulated microorganism isobtained.

In step (2′) of the second embodiment, it is not required to supply theelectron donor B since the metal ion is directly adsorbed on themicroorganism.

The microorganism is preferably iron-reducing bacteria as in the firstembodiment, and, among the iron-reducing bacteria, the genus Shewanellaalgae is more preferable and Shewanella algae and Shewanella oneidensisare even more preferable from the viewpoint of favorable adsorptionefficiency of the metal ion.

The ratio of the amounts of the metal ion-containing solution W₀ and thebacterial culture A₀ supplied to the reaction solution storage tank 10may be set such that the theoretical initial concentrations thereof inthe reaction solution (microorganism cell suspension) in the reactionsolution storage tank 10 become a suitable condition in a case in whichthe metal ion is directly adsorbed on the microorganism.

The theoretical initial concentration of the metal ion in the reactionsolution in the reaction solution storage tank 10 is preferably from0.01 to 10 mM and more preferably from 0.1 to 5 mM from the viewpointthat the efficiency to adsorb the metal ion on the microorganism is morefavorable.

The theoretical initial concentration of the bacterial culture in thereaction solution in the reaction solution storage tank 10 is preferablyfrom 5.0×10¹² to 5.0×10¹⁶ cells/m³ and more preferably from 5.0×10¹³ to1.0×10¹⁶ cells/m³ from the viewpoint that the efficiency to adsorb themetal ion on the microorganism is more favorable.

Step (1′) may be performed by a batch reaction or by a semi-batchreaction.

In the case of performing step (1′) by a semi-batch reaction, it ispreferable that the supply of the metal ion-containing solution W₀ andthe bacterial culture A₀ to the reaction solution storage tank 10 isadjusted in the range in which the reaction solution in the reactionsolution storage tank 10 can be maintained in a predetermined amount inconsideration of the amount of the solution W₁ containing the metal ionaccumulated microorganism which is transferred to the concentration unit3. The supply of the metal ion-containing solution W₀ and the bacterialculture A₀ to the reaction solution storage tank 10 may be continuous orintermittent as long as the reaction solution in the reaction solutionstorage tank 10 can be maintained in a predetermined amount.

(Step (2′))

Step (2′) can be performed in the same manner as step (2) of the firstembodiment.

(Step (3′))

Step (3′) can be performed in the same manner as step (3) of the firstembodiment. The cell concentration of the solution W₁ containing themetal ion accumulated microorganism in the reaction solution storagetank 10 increases as the concentrated solution W₂ obtained in step (2′)is returned to the reaction solution storage tank 10 of step (1′) to becirculated.

(Step (4′))

In step (4′), the solution W₁ containing the metal ion accumulatedmicroorganism is recovered from the reaction solution storage tank 10 soas to have a cell concentration of 1.0×10¹⁷ cells/m³ or less. It ispossible to recover the metal ion by recovering the metal ionaccumulated microorganism.

The cell concentration of the solution W₁ containing the metal ionaccumulated microorganism which is recovered from the reaction solutionstorage tank 10 is 1.0×10¹⁷ cells/m³ or less, preferably from 1.0×10¹⁵to 1.0×10¹⁷ cells/m³ and more preferably from 5.0×10¹⁶ to 1.0×10¹⁷cells/m³. The concentration efficiency of metal is more favorable whenthe cell concentration is equal to or greater than the lower limitvalue. It is easy to continuously favorably maintain the solid-liquidseparation by membrane separation as well as the treatment efficiency ofthe metal ion-containing solution is more favorable when the cellconcentration is equal to or less than the upper limit value.

The application of the recovered metal is not particularly limited. Therecovered metal compound may be used after baking the metal ionaccumulated microorganism in an electric furnace or the like so as toremove the microorganism and impurities.

In the method for metal concentration according to the second embodimentof the invention described above, a portion of the solution W₁containing the metal ion accumulated microorganism which is obtained instep (1′) is concentrated by membrane filtration in step (2′) andreturned to step (1′) to be circulated in step (3′), and thus it ispossible to increase the concentration of the metal ion accumulatedmicroorganism, namely, the concentration of the metal ion. Hence, it ispossible to recover the metal from the metal ion-containing solutionwith high efficiency. In addition, the pH control is also easy since itis not required to convert the metal ion contained in the metalion-containing solution into a hydroxide in order to recover the metal,and thus the operation is convenient.

Incidentally, the method for metal recovery of the second embodiment ofthe invention is not limited to the method using the device for metalrecovery 1 described above. For example, it may be a method in which thereaction to directly adsorb a metal ion in a metal ion-containingsolution on a microorganism in the reaction solution storage tank isconducted in the pipe of the preceding stage of the reaction solutionstorage tank by mixing a metal ion-containing solution and amicroorganism.

In addition, it may be a method using a device (device for metalrecovery 1′) in which the reaction solution storage tank is separatelyprovided as a reaction tank and a concentration tank as illustrated inFIG. 2, for example.

For example, in the case of using the device for metal recovery 1′, therecovery of the solution containing the microorganism having the metalion adsorbed thereon can be conducted by the same method as that for thesolution containing the microorganism having the metal fine particleaccumulated therein in the first embodiment.

In the method for metal recovery using the device for metal recovery 1′,the metal ion-containing solution W₀ and the bacterial culture A₀ aresupplied to the reaction solution storage tank 10′, and themicroorganism contained in the bacterial culture A₀ is allowed to act onthe metal ion-containing solution W₀ so as to adsorb the metal ion inthe metal ion-containing solution W₀ on the microorganism in thereaction solution storage tank 10′. In addition, the solution W₁ thatcontains the microorganism having the metal ion adsorbed thereon istransferred to the concentration tank 12 while allowing themicroorganism to act on the metal ion-containing solution W₀.

Specifically, while stirring with the stirring blade 10 a, to thereaction solution storage tank 10′, the metal ion-containing solution W₀is supplied from the metal ion-containing solution storage tank 20through the pipe 50 and the bacterial culture A₀ is supplied from thebacterial culture storage tank 22 through the pipe 52. In addition, aportion of the solution W₁ that contains the microorganism having themetal ion adsorbed thereon is continuously withdrawn and transferred tothe concentration tank 12 through the pipe 42 while conducting theadsorption of the metal ion by the microorganism in the reactionsolution storage tank 10′.

In addition, in a case in which it is required to remove oxygen in thesolution upon directly adsorbing the metal ion contained in the metalion-containing solution on the microorganism, it may be a method inwhich the removal of oxygen is conducted in at least either of thereaction solution storage tank or the preceding stage of the reactionsolution storage tank.

EXAMPLES

Hereinafter, the invention will be described in detail with reference toexamples, but the invention is not limited by the following description.

[Preparation of Bacterial Culture]

As the microorganism, Shewanella algae (51181 strain) or Shewanellaoneidensis (700550 strain) sold by the American Type Culture Collection(ATCC) of a culture collection institute was used. The microorganism wascultured in a Tryptic Soy Broth (TSB) liquid medium while shaking at 30°C. and culturing was stopped in the logarithmic growth phase. Thecultured cells were collected by centrifugation, the supernatant wasthen removed, and the collected cells were resuspended in a 50 mMpotassium-sodium phosphate buffer solution (pH 7.0). The washingoperation to remove the supernatant by subjecting the resuspended cellsthus obtained to centrifugation was repeated two times and the washedcells were then resuspended in the buffer, whereby the bacterial culturewas prepared.

[Filtration Membrane]

As the filtration membrane of the membrane module 14, a compositemembrane (outer diameter: 2.8 mm, nominal pore size: 0.05 μm,manufactured by Mitsubishi Rayon Co., Ltd.) made of a polyvinylidenefluoride (PVDF) resin was used.

As the membrane filter, a film (MF-Millipore, diameter: 47 mm, nominalpore size: 0.05 μm, manufactured by Merck Ltd.) made of a cellulosemixed ester was used.

[Metal Concentration]

The concentration of metal in the solution was measured by ICP atomicemission spectrophotometry. An ICP atomic emission spectrophotometer(Shimadzu Corporation, ICEP-9000) was used as the apparatus formeasurement.

[Cell Concentration]

The cell concentration in the solution was measured by aspectrophotometer for ultraviolet and visible region.

Example 1

To the reaction solution storage tank 10 of the device for metalrecovery 1 illustrated in FIG. 1, 25 mL of an aqueous solution of 10 mMpalladium(II) chloride, 20 mL of an aqueous solution of 125 mM sodiumformate that was the electron donor and 5 mL of bacterial culture of1.0×10¹⁶ cells/m³ Shewanella algae (S. algae) were supplied such thatthe theoretical initial concentration of the reaction solution becamethe following condition, and it was 50 mL in total.

Concentration of Pd(II): 5 mM (530 ppm by mass)

Concentration of sodium formate: 50 mM and

Concentration of cells (S. algae): 1.0×10¹⁵ cells/m³

The inside of the reaction solution storage tank 10 was stirred at 30°C. and the reduction and accumulation reaction was conducted. After 5minutes from the start of the reaction, the cells became black as wellas the reaction solution which was originally yellow became colorless,and thus the situation was observed that the Pd fine particles wereaccumulated in the microorganism. After 5 minutes from that moment(after 10 minutes from the start of the reaction), a portion of thesolution W₁ containing the Pd fine particle accumulated microorganismwas sampled and filtered through a membrane filter having a nominal poresize of 0.05 μm. The concentration of Pd(II) in the filtrate obtainedhere was measured and the result was about 1 ppm by mass.

Subsequently, a portion the solution W₁ containing the Pd fine particleaccumulated microorganism was continuously transferred to the membranemodule 14 and separated into the concentrated solution W₂ and thefiltered water W₃ by membrane filtration while supplying 150 mL of anaqueous solution of 10 mM palladium(II) chloride per hour and 150 mL ofan aqueous solution of 100 mM sodium formate per hour to the reactionsolution storage tank 10. The concentrated solution W₂ was returned tothe reaction solution storage tank 10 so as to concentrate the Pd fineparticle accumulated microorganism in the reaction solution storage tank10. At this time, the withdrawal rate of the filtered water W₃ was setto 300 mL per hour and the amount of the solution W₁ containing the Pdfine particle accumulated microorganism in the reaction solution storagetank 10 was maintained at 50 mL so that the average hydraulic retentiontime (HRT) of the reaction solution was 10 minutes. The transfer rate ofthe solution W₁ from the reaction solution storage tank 10 to themembrane module 14 was 160 L/hr, the filtration linear velocity (LV) was0.25 m/day, and the return rate of the concentrated solution W₂ from themembrane module 14 to the reaction solution storage tank 10 was 159.7L/hr.

After 4.5 hours from the start of membrane filtration, the concentrationof Pd(II) in the filtered water W₃ was measured and the result was about1 ppm by mass. From this fact, it was understood that 99% or more ofPd(II) contained in the aqueous solution of 10 mM palladium(II) chloridewas accumulated as intracellular fine particles in the reaction solutionstorage tank 10 and the membrane module 14. In addition, theconcentration of Pd(II) in the solution W₁ containing the Pd fineparticle accumulated microorganism in the reaction solution storage tank10 was 140 mM (14840 ppm by mass) and thus the solution W₁ wasconcentrated to be 14 times the initial aqueous solution of 10 mMpalladium(II) chloride. In addition, the cell concentration of thesolution W₁ was 1.0×10¹⁵ cells/m³. It was understood that 128 g of Pdfine particles per 1 g of dry cells was accumulated since the number ofcells per 1 g of dry cells was 8.58×10¹².

Example 2

To the reaction solution storage tank 10 of the device for metalrecovery 1, 240 mL of an aqueous solution of 1.25 mM palladium(II)chloride, 30 mL of an aqueous solution of 500 mM sodium formate and 30mL of bacterial culture of 1.0×10¹⁶ cells/m³ S. algae were supplied suchthat the theoretical initial concentration of the reaction solutionbecame the following condition, and it was 300 mL in total.

Concentration of Pd(II): 1 mM (106 ppm by mass)

Concentration of sodium formate: 50 mM and

Concentration of cells (S. algae): 1.0×10¹⁵ cells/m³

The inside of the reaction solution storage tank 10 was stirred at 30°C. and the reduction and accumulation reaction was conducted. After 30minutes from the start of the reaction, the cells became black as wellas the reaction solution which was originally yellow became colorless,and thus the situation was observed that the Pd fine particles wereaccumulated in the microorganism. After 30 minutes from that moment(after 1 hour from the start of the reaction), a portion of the solutionW₁ containing the Pd fine particle accumulated microorganism was sampledand filtered through a membrane filter having a nominal pore size of0.05 μm. The concentration of Pd(II) in the filtrate obtained here wasmeasured and the result was about 1 ppm by mass.

Subsequently, a portion the solution W₁ containing the Pd fine particleaccumulated microorganism was continuously transferred to the membranemodule 14 and separated into the concentrated solution W₂ and thefiltered water W₃ by membrane filtration, and the concentrated solutionW₂ was returned to the reaction solution storage tank 10 so as toconcentrate the Pd fine particle accumulated microorganism in thereaction solution storage tank 10 under the condition presented in Table1 while supplying an aqueous solution of palladium(II) chloride, anaqueous solution of sodium formate and the bacterial culture of S. algaeto the reaction solution storage tank 10 under the supply conditionpresented in Table 1.

After 9 hours from the start of membrane filtration, the concentrationof Pd(II) in the filtered water W₃ was measured and the result was about1 ppm by mass. From this fact, it was understood that 99% or more ofpalladium contained in the aqueous solution of 1.25 mM palladium(II)chloride was accumulated as intracellular fine particles in the reactionsolution storage tank 10 and the membrane module 14. In addition, theconcentration of Pd(II) in the solution W₁ containing the Pd fineparticle accumulated microorganism in the reaction solution storage tank10 was 10 mM (1060 ppm by mass) and thus the solution W₁ wasconcentrated to be 8 times the aqueous solution of 1.25 mM palladium(II)chloride. In addition, the cell concentration of the solution W₁ was1.0×10¹⁶ cells/m³. It was understood that 0.91 g of Pd fine particlesper 1 g of dry cells was accumulated since the number of cells per 1 gof dry cells was 8.58×10¹².

Example 3

The pellets of the Pd fine particle accumulated microorganism wereobtained by subjecting 50 mL of the solution containing the Pd fineparticle accumulated microorganism obtained in Example 1 tocentrifugation. The entire amount of the pellets was introduced into thereaction solution storage tank 10 of the device for metal recovery 1illustrated in FIG. 1, and 40 mL of an aqueous solution of 1.25 mMpalladium(II) chloride, 5 mL of an aqueous solution of 500 mM sodiumformate and 5 mL of bacterial culture of 1.0×10¹⁶ cells/m³ S. algae werethen supplied thereto and it was 50 mL in total. The theoretical initialconcentration of the reaction solution at this time was as follows.

Concentration of Pd(II): 1 mM (106 ppm by mass)

Concentration of sodium formate: 50 mM

Concentration of cells (S. algae): 1.0×10¹⁵ cells/m³

Concentration of Pd fine particle accumulated microorganism: 1.0×10¹⁵cells/m³ and

Concentration of Pd(II) accumulated in microorganism: 140 mM

The inside of the reaction solution storage tank 10 was stirred at 30°C. and the reduction and accumulation reaction was conducted. After 5minutes from the start of the reaction, a portion of the solution W₁containing the Pd fine particle accumulated microorganism was sampledand filtered through a membrane filter having a nominal pore size of0.05 μm. The concentration of Pd(II) in the filtrate obtained here wasmeasured and the result was about 1 ppm by mass.

Subsequently, a portion the solution W₁ containing the Pd fine particleaccumulated microorganism was continuously transferred to the membranemodule 14 and separated into the concentrated solution W₂ and thefiltered water W₃ by membrane filtration, and the concentrated solutionW₂ was returned to the reaction solution storage tank 10 so as toconcentrate the Pd fine particle accumulated microorganism in thereaction solution storage tank 10 under the condition presented in Table1 while supplying an aqueous solution of palladium(II) chloride, anaqueous solution of sodium formate and the bacterial culture of S. algaeto the reaction solution storage tank 10 under the supply conditionpresented in Table 1.

After 9 hours from the start of membrane filtration, the concentrationof Pd(II) in the filtered water W₃ was measured and the result was about1 ppm by mass. From this fact, it was understood that 99% or more ofPd(II) contained in the aqueous solution of 1.25 mM palladium(II)chloride was accumulated as intracellular fine particles in the reactionsolution storage tank 10 and the membrane module 14. The concentrationof Pd(II) of the solution W₁ containing the Pd fine particle accumulatedmicroorganism in the reaction solution storage tank 10 was 194 mM. Theconcentration of Pd(II) accumulated in the microorganism was 54 mM (5724ppm by mass) when the content of the Pd fine particle accumulatedmicroorganism which was previously introduced was excluded, and thus thesolution W₁ was concentrated to be 43.2 times the aqueous solution of1.25 mM palladium(II) chloride. In addition, the cell concentration ofthe reaction solution was 5.5×10¹⁶ cells/m³ and it was 5.4×10¹⁶ cells/m³when the content of the Pd fine particle accumulated microorganism whichwas previously introduced was excluded. It was understood that 0.91 g ofPd fine particles per 1 g of dry cells was accumulated when the contentof the Pd fine particle accumulated microorganism which was previouslyintroduced was excluded since the number of cells per 1 g of dry cellswas 8.58×10¹².

Thereafter, the supply of the aqueous solution of palladium(II)chloride, the aqueous solution of sodium formate, and the bacterialculture of S. algae was stopped and the membrane filtration and thereturn of the concentrated solution were continued. After 5 minutes fromthe stop of the liquid supply, clogging of the membrane occurred, thetransmembrane pressure difference (ΔP) was higher than 50 kPa at thetime at which the amount of the solution W₁ containing Pd fine particleaccumulated microorganism that was contained in the reaction solutionstorage tank 10 was 25 mL, and thus the operation was stopped. At thistime, the cell concentration in the reaction solution storage tank 10was 1.1×10¹⁷ cells/m³.

Example 4

To the reaction solution storage tank 10 of the device for metalrecovery 1, 240 mL of an aqueous solution of 1.25 mM platinum(IV) sodiumchloride, 30 mL of an aqueous solution of 330 mM sodium lactate and 30mL of bacterial culture of 1.0×10¹⁶ cells/m³ S. algae were supplied suchthat the theoretical initial concentration of the reaction solutionbecame the following condition, and it was 300 mL in total.

Concentration of Pt(IV): 1 mM (195 ppm by mass)

Concentration of sodium lactate: 33 mM and

Concentration of cells (S. algae): 1.0×10¹⁵ cells/m³

The inside of the reaction solution storage tank 10 was stirred at 30°C. and the reduction and accumulation reaction was conducted. After 1hour from the start of the reaction, a portion of the solution W₁containing the Pt fine particle accumulated microorganism was sampledand filtered through a membrane filter having a nominal pore size of0.05 μm. The concentration of Pt(IV) in the filtrate obtained here wasmeasured and the result was about 20 ppm by mass.

Subsequently, a portion the solution W₁ containing the Pt fine particleaccumulated microorganism was continuously transferred to the membranemodule 14 and separated into the concentrated solution W₂ and thefiltered water W₃ by membrane filtration, and the concentrated solutionW₂ was returned to the reaction solution storage tank 10 so as toconcentrate the Pt fine particle accumulated microorganism in thereaction solution storage tank 10 under the condition presented in Table1 while supplying an aqueous solution of platinum(IV) sodium chloride,an aqueous solution of sodium lactate and the bacterial culture of S.algae to the reaction solution storage tank 10 under the supplycondition presented in Table 1.

After 9 hours from the start of membrane filtration, the concentrationof Pt(IV) in the filtered water W₃ was measured and the result was about20 ppm by mass. From this fact, it was understood that about 90% ofplatinum contained in the aqueous solution of 1.25 mM platinum(IV)sodium chloride was accumulated as intracellular fine particles in thereaction solution storage tank 10 and the membrane module 14. Inaddition, the concentration of Pt(IV) in the solution W₁ containing thePt fine particle accumulated microorganism in the reaction solutionstorage tank 10 was 9 mM (1755 ppm by mass) and thus the solution W₁ wasconcentrated to be 7.2 times the aqueous solution of 1.25 mMplatinum(IV) sodium chloride. In addition, the cell concentration of thesolution W₁ was 1.0×10¹⁶ cells/m³, and thus it was understood that 1.5 gof Pt fine particles per 1 g of dry cells was accumulated since thenumber of cells per 1 g of dry cells was 8.58×10¹².

Example 5

The reduction and accumulation reaction and concentration of palladiumwere conducted using the device for metal recovery 1 under the conditionpresented in Table 2 in the same manner as in Example 2 except that themicroorganism was changed to Shewanella oneidensis (S. oneidensis).

After 9 hours from the start of membrane filtration, the concentrationof Pd(II) in the filtered water W₃ was measured and the result was about5 ppm by mass. From this fact, it was understood that about 95% ofPd(II) contained in the aqueous solution of 1.25 mM palladium(II)chloride was accumulated as intracellular fine particles in the reactionsolution storage tank 10 and the membrane module 14. In addition, theconcentration of Pd(II) in the solution W₁ containing the Pd fineparticle accumulated microorganism in the reaction solution storage tank10 was 9.5 mM (1007 ppm by mass) and thus the solution W₁ wasconcentrated to be 7.6 times the aqueous solution of 1.25 mMpalladium(II) chloride. In addition, the cell concentration of thesolution W₁ was 1.0×10¹⁶ cells/m³, and thus it was understood wasunderstood that 0.86 g of Pd fine particles per 1 g of dry cells wasaccumulated since the number of cells per 1 g of dry cells was8.58×10¹².

Example 6

Using the device for metal recovery 1, 346.5 mL of an aqueous solutionof 1.1 mM gallium(III) chloride and 38.5 mL of bacterial culture of7.0×10¹⁶ cells/m³ S. algae were supplied such that the theoreticalinitial concentration of the reaction solution in the reaction solutionstorage tank 10 became the following condition, and it was 385 mL intotal.

Concentration of Ga(III): 1 mM (70 ppm by mass)

Concentration of cells (S. algae): 1.0×10¹⁵ cells/m³

The inside of the reaction solution storage tank 10 was stirred at 30°C. and the reduction and accumulation reaction was conducted. After 77minutes from the start of the reaction, a portion of the solution W₁containing the Ga(III) ion accumulated microorganism was sampled andfiltered through a membrane filter having a nominal pore size of 0.05μm. The concentration of Ga(III) in the filtrate obtained here wasmeasured and the result was about 0.1 ppm by mass.

Subsequently, a portion the solution W₁ containing the Ga(III) ionaccumulated microorganism was continuously transferred to the membranemodule 14 and separated into the concentrated solution W₂ and thefiltered water W₃ by membrane filtration, and the concentrated solutionW₂ was returned to the reaction solution storage tank 10 so as toconcentrate the Ga(III) ion accumulated microorganism in the reactionsolution storage tank 10 under the condition presented in Table 1 whilesupplying an aqueous solution of gallium(III) chloride and the bacterialculture of S. algae to the reaction solution storage tank 10 under thesupply condition presented in Table 2. The transmembrane pressuredifference (ΔP) was from 10 to 20 kPa.

After 11.8 hours from the start of membrane filtration, theconcentration of Ga(III) in the filtered water W₃ was measured and theresult was about 0.1 ppm by mass. From this fact, it was understood that99% or more of Ga(III) ion contained in the aqueous solution of 1.1 mMgallium(III) chloride was accumulated as intracellular ions in thereaction solution storage tank 10 and the membrane module 14. Theconcentration of Ga(III) in the solution W₁ containing the Ga(III) ionaccumulated microorganism in the reaction solution storage tank 10 was10 mM (700 ppm by mass) and thus the solution W₁ was concentrated to be9.1 times the aqueous solution of 1.1 mM gallium(III) chloride. Inaddition, the cell concentration of the solution W₁ was 7.0×10¹⁶cells/m³, and thus it was understood that 0.085 g of Ga(III) per 1 g ofdry cells was accumulated.

Thereafter, the solution W₁ containing the Ga(III) ion accumulatedmicroorganism was recovered from the reaction solution storage tank 10to the recovery unit 16 by 30 mL per hour. At this time, the supply ofthe aqueous solution of gallium(III) chloride and the bacterial cultureof S. algae, the membrane filtration and the return of the concentratedsolution were continued, and the withdrawal rate of the filtered waterW₃ was set to 270 mL per hour and the amount of the solution W₁containing the Ga(III) ion accumulated microorganism that was containedin the reaction solution storage tank 10 was maintained at 385 mL. Thetransmembrane pressure difference (ΔP) was from 10 to 20 kPa for 10hours or longer in this state.

Thereafter, the supply of the aqueous solution of gallium(III) chlorideand the bacterial culture of S. algae and the recovery to the recoverunit 16 were stopped and the membrane filtration and the return of theconcentrated solution were continued. After 30 minutes from the stop ofthe liquid supply, clogging of the membrane occurred, the transmembranepressure difference (ΔP) was higher than 50 kPa at the time at which theamount of the solution W₁ containing the Ga(III) ion accumulatedmicroorganism that was contained in the reaction solution storage tank10 was 245 mL, and thus the operation was stopped. At this time, thecell concentration of the reaction solution in the reaction solutionstorage tank 10 was 1.1×10¹⁷ cells/m³.

Example 7

The accumulation and concentration of In(III) were conducted using thedevice for metal recovery 1 under the conditions presented in Table 2 inthe same manner as in Example 6 except that the cells were S. oneidensisand the metal ion-containing solution was 1.1 mM indium(III) chloride.

After 11.8 hours from the start of membrane filtration, theconcentration of In(III) in the filtered water W₃ was measured and theresult was about 0.1 ppm by mass. From this fact, it was understood that99% or more of In(III) contained in the aqueous solution of 1.1 mMindium(III) chloride was accumulated as intracellular ions in thereaction solution storage tank 10 and the membrane module 14. Theconcentration of In(III) in the solution W₁ containing the In(III) ionaccumulated microorganism in the reaction solution storage tank 10 was10 mM (1140 ppm by mass) and thus the solution W₁ was concentrated to be9.1 times the aqueous solution of 1.1 mM indium(III) chloride. Inaddition, the cell concentration of the solution W₁ was 7.0×10¹⁶cells/m³, and thus it was understood that 0.14 g of In(III) per 1 g ofdry cells was accumulated.

Thereafter, the solution W₁ containing the In(III) ion accumulatedmicroorganism was recovered from the reaction solution storage tank 10to the recovery unit 16 by 30 mL per hour. At this time, the supply ofthe aqueous solution of indium(III) chloride and the bacterial cultureof S. oneidensis, the membrane filtration and the return of theconcentrated solution were continued, and the withdrawal rate of thefiltered water W₃ was set to 270 mL per hour and the amount of thesolution W₁ containing the In(III) ion accumulated microorganism thatwas contained in the reaction solution storage tank 10 was maintained at385 mL. The transmembrane pressure difference (ΔP) was from 10 to 20 kPafor 10 hours or longer in this state.

Thereafter, the supply of the aqueous solution of indium(III) chlorideand the bacterial culture of S. oneidensis and the recovery to therecover unit 16 were stopped and the membrane filtration and the returnof the concentrated solution were continued. After 30 minutes from thestop of the liquid supply, clogging of the membrane occurred, thetransmembrane pressure difference (ΔP) was higher than 50 kPa at thetime at which the amount of the solution W₁ containing In(III) ionaccumulated microorganism that was contained in the reaction solutionstorage tank 10 was 245 mL, and thus the operation was stopped. At thistime, the cell concentration in the reaction solution storage tank 10was 1.1×10¹⁷ cells/m³.

Example 8

Using the device for metal recovery 1′ illustrated in FIG. 2, a Pd(II)containing solution, sodium formate that was the electron donor and thebacterial culture were continuously supplied such that the theoreticalinitial concentration of the reaction solution (microorganism cellsuspension) in the reaction tank 10′ became the following condition.

Concentration of Pd(II): 1 mM

Concentration of sodium lactate: 50 mM and

Concentration of cells: 5.0×10¹⁵ cells/m³.

The solution W₁ containing the Pd fine particle accumulatedmicroorganism was continuously withdrawn and transferred to theconcentration tank 12 so that the average hydraulic retention time (HRT)of the reaction solution in the reaction tank 10′ was 60 minutes, thesolution W₁ was separated into the concentrated solution W₂ and thefiltered water W₃ in the concentration tank 12 by being subjected tomembrane filtration by the membrane module 14 so as to concentrate thecells. The filtration linear velocity (LV) for membrane filtration was0.25 m/day.

The concentration of Pd(II) in the filtered water W₃ was measured, andthe ratio of the concentration of Pd(II) in the filtered water W₃ to theconcentration of Pd(II) in the reaction tank 10′ was determined as thePd recovery percentage. As a result, 94% or more of Pd(II) introducedinto the reaction tank 10′ was recovered in the cells. The operatingconditions and the results are presented in Table 3.

Example 9

Using the device for metal recovery 1′ illustrated in FIG. 2, a Pd(II)containing solution, sodium formate that was the electron donor and thebacterial culture were continuously supplied so that the theoreticalinitial concentration of the reaction solution (microorganism cellsuspension) in the reaction tank 10′ became the following condition.

Concentration of Pd(II): 1 mM

Concentration of sodium formate: 200 mM and

Concentration of cells: 1.0×10¹⁵ cells/m³

The solution W₁ containing the Pd fine particle accumulatedmicroorganism was continuously withdrawn and transferred to theconcentration tank 12 so that the average hydraulic retention time (HRT)of the reaction solution in the reaction tank 10′ was 10 minutes, thesolution W₁ was separated into the concentrated solution W₂ and thefiltered water W₃ in the concentration tank 12 by being subjected tomembrane filtration by the filtration membrane so as to concentrate thecells. The filtration linear velocity (LV) for membrane filtration was0.25 m/day.

The concentration of Pd(II) in the filtered water W₃ was measured, andthe ratio of the concentration of Pd(II) in the filtered water W₃ to theconcentration of Pd(II) in the reaction tank 10′ was determined as thePd recovery percentage. The concentration of Pd(II) in the filteredwater W₃ was measured, but the result was equal to or less than thedetection limit (0.1 ppm by mass), and thus 99.8% or more of Pdintroduced into the reaction tank 10′ was recovered in the cells. Theoperating conditions and the results are presented in Table 3.

Example 10

Using the device for metal recovery 1′ illustrated in FIG. 2, a Gacontaining solution and a bacterial culture were continuously suppliedso that the theoretical initial concentration of the reaction solution(microorganism cell suspension) in the reaction tank 10′ became thefollowing condition.

Concentration of Ga(III): 0.5 mM and

Concentration of cells: 0.7×10¹⁶ cells/m³

The solution W₁ that contained the microorganism having Ga(III) ionadsorbed thereon was continuously withdrawn and transferred to theconcentration tank 12 so that the average hydraulic retention time (HRT)of the reaction solution in the reaction tank 10′ was 77 minutes, thesolution W₁ was separated into the concentrated solution W₂ and thefiltered water W₃ in the concentration tank 12 by being subjected tomembrane filtration by the membrane module 14 so as to concentrate thecells. The filtration linear velocity (LV) for membrane filtration was0.25 m/day.

The concentration of Ga(III) in the filtered water W₃ was measured, andthe ratio of the concentration of Ga(III) in the filtered water W₃ tothe concentration of Ga(III) in the reaction tank 10′ was determined asthe Ga recovery percentage. The concentration of Ga(III) in the filteredwater W₃ was measured, but the result was equal to or less than thedetection limit (0.1 ppm by mass), and thus 99.8% or more of Ga(III)introduced into the reaction tank 10′ was recovered in the cells. Theoperating conditions and the results are presented in Table 3.

Comparative Example 1

The reduction and accumulation reaction and concentration of palladiumwere conducted using the device for metal recovery 1 under theconditions presented in Table 3 in the same manner as in Example 1except that the membrane module 14 was changed to a suction filter usinga membrane filter, the transfer rate of the solution to the filter andthe withdrawal rate of the filtered water W₃ were set to 300 mL per hourand the Pd fine particle accumulated microorganism to be obtained wasnot returned to the reaction solution storage tank 10.

After 4.5 hours from the start of membrane filtration, the concentrationof Pd(II) in the filtered water W₃ was measured and the result was about500 ppm by mass. From this fact, it was understood that about 95% ofPd(II) contained in the aqueous solution of 10 mM Palladium(II) chloridewas discharged to the outside of the system as the filtered water W₃.The accumulated amount of palladium per 1 g of cells was 10.9 g, but itwas considered that most of palladium accumulated in cells was thosewhich were accumulated at the time of the initial reduction andaccumulation reaction. It was indicated that the recovery percentagefrom the solution and the accumulated amount of palladium per 1 g ofcells were remarkably decreased as compared with Example 1 in which thePd fine particle accumulated microorganism was returned.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Reduction and Species ofmicroorganism S. algae S. algae S. algae S. algae accumulation stepInitial Initial concentration of cells [cells/m³] 1.0 × 10¹⁵ 1.0 × 10¹⁵1.0 × 10¹⁵ 1.1 × 10¹⁵ conditions Initial concentration of metal ion [mM]5 1 1 1 Initial concentration of electron donor [mM] 50 50 50 33 SupplyBacterial Concentration [cells/m³] — 1.0 × 10¹⁶ 1.0 × 10¹⁶ 1.1 × 10¹⁶conditions culture Supply rate [mL/hr] — 30 30 30 Metal ion- Kind ofmetal compound PdCl₂ PdCl₂ PdCl₂ Na₂PtCl₆ containing Concentration [mM]10 1.25 1.25 1.25 solution Supply rate [mL/hr] 150 240 240 240 Electrondonor- Kind of electron donor Na formate Na formate Na formate Nalactate containing Concentration [mM] 100 500 500 330 solution Supplyrate [mL/hr] 150 30 30 30 Presence or absence of addition of reducingmetal Absence Absence Presence Absence Amount of solution maintained inreaction solution storage tank [mL] 50 300 50 300 Hydraulic retentiontime of microorganism cell suspension (HRT)[min] 10 60 10 60Concentration step Transfer rate of solution W₁ to concentration unit[L/hr] 160 160 160 160 Before start Withdrawal rate of filtered water[mL/hr] 300 300 300 300 of recovery Filtration linear velocity(LV)[m/day] 0.25 0.25 0.25 0.25 After start Withdrawal rate of filteredwater [mL/hr] — — — — of recovery Filtration linear velocity (LV)[m/day]— — — — Return step Return rate of concentrated solution W₂ [L/hr] 159.7159.7 159.7 159.7 Recovery step Start time of recovery (after start offiltration) [hours] 4.5 9 9 9 Concentration of metal ion in filteredwater W₃ [mM] 0.01 0.01 0.01 0.1 Recovery percentage of metal[%] >99 >99 >99 90 Recovery rate [mL/hr] — — — — Concentration of cellsin solution W₁ at the time of recovery [cells/m³] 1.0 × 10¹⁵ 1.0 × 10¹⁶1.0 × 10¹⁶ 1.1 × 10¹⁶ Concentration of metal in solution W₁ at the timeof recovery [mM] 140 10 54 9 Accumulated amount of metal per 1 g of drycells [g] 128 0.91 0.91 1.5

TABLE 2 Example 5 Example 6 Example 7 Reduction and Species ofmicroorganism S. oneidensis S. algae S. oneidensis accumulation stepInitial Initial concentration of cells [cells/m³] 1.0 × 10¹⁵ 7.0 × 10¹⁵7.0 × 10¹⁵ conditions Initial concentration of metal ion [mM] 1 1 1Initial concentration of electron donor [mM] 50 — — Supply BacterialConcentration [cells/m³] 1.0 × 10¹⁶ 7.0 × 10¹⁶ 7.0 × 10¹⁶ conditionsculture Supply rate [mL/hr] 30 30 30 Metal ion- Kind of metal compoundPdCl₂ GaCl₃ InCl₃ containing Concentration [mM] 1.25 1.1 1.1 solutionSupply rate [mL/hr] 240 270 270 Electron donor- Kind of electron donorNa formate — — containing Concentration [mM] 500 — — solution Supplyrate [mL/hr] 30 — — Presence or absence of addition of reducing metalAbsence Absence Absence Amount of solution in reaction solution storagetank [mL] 300 385 385 Hydraulic retention time of microorganism cellsuspension (HRT)[min] 60 77 77 Concentration step Transfer rate ofsolution W₁ to concentration unit [L/hr] 160 160 160 Before startWithdrawal rate of filtered water [mL/hr] 300 300 300 of recoveryFiltration linear velocity (LV)[m/day] 0.25 0.25 0.25 After startWithdrawal rate of filtered water [mL/hr] — 270 270 of recoveryFiltration linear velocity (LV)[m/day] — 0.23 0.23 Return step Returnrate of concentrated solution W₂ [L/hr] 159.7 159.7 159.7 Recovery stepStart time of recovery [hours] 9 11.8 11.8 Concentration of metal ion infiltered water W₃ [mM] 0.01 0.005 0.005 Recovery percentage of metal [%]95 >99 >99 Recovery rate [mL/hr] — 30 10 Concentration of cells insolution W₁ at the time of recovery [cells/m³] 1.0 × 10¹⁶ 7.0 × 10¹⁶ 30Concentration of metal in solution W₁ at the time of recovery [mM] 9.510 10 Accumulated amount of metal per 1 g of cells [g] 0.86 0.085 0.14

TABLE 3 Comparative Example 8 Example 9 Example 10 Example 1 Reductionand Species of microorganism S. algae S. algae S. algae S. algaeaccumulation step Initial Initial concentration of cells [cells/m³] 5.0× 10¹⁵ 1.0 × 10¹⁵ 7.0 × 10¹⁵ 1.0 × 10¹⁵ conditions Initial concentrationof metal ion [mM] 1 1 0.5 5 Initial concentration of electron donor [mM]50 200 — 50 Supply Bacterial Concentration [cells/m³] 5.0 × 10¹⁶ 1.0 ×10¹⁶ 7.0 × 10¹⁶ — conditions culture Supply rate [mL/hr] 30 30 30 —Metal ion- Kind of metal compound PdCl₂ PdCl₂ GaCl₃ PdCl₂ containingConcentration [mM] 1.25 1.25 0.55 10 solution Supply rate [mL/hr] 240240 270 150 Electron donor- Kind of electron donor Na formate Na formate— Na formate containing Concentration [mM] 500 2000 — 100 solutionSupply rate [mL/hr] 30 30 — 150 Presence or absence of addition ofreducing metal Absence Absence Absence Absence Amount of solutionmaintained in reaction solution storage tank [mL] 300 50 385 50Hydraulic retention time of reaction solution (HRT)[min] 60 10 77 10Concentration step Transfer rate of solution W₁ to concentration unit[L/hr] 160 160 160 0.3 Before start Withdrawal rate of filtered water[mL/hr] 300 300 300 300 of recovery Filtration linear velocity(LV)[m/day] 0.25 0.25 0.25 — After start Withdrawal rate of filteredwater [mL/hr] — — 270 — of recovery Filtration linear velocity(LV)[m/day] — — 0.23 — Return step Return rate of concentrated solutionW₂ [L/hr] 159.7 159.7 159.7 — Recovery step Start time of recovery(after start of filtration) [hours] 9 9 11.8 4.5 Concentration of metalion in filtered water W₃ [mM] 0.01 0.01 0.005 4.7 Recovery percentage ofmetal [%] >94 >99.8 >99.8 5 Recovery rate [mL/hr] — — 30 — Concentrationof cells in solution W₁ at the time of recovery [cells/m³] 5.0 × 10¹⁶1.0 × 10¹⁶ 7.0 × 10¹⁶ — Concentration of metal in solution W₁ at thetime of recovery [mM] 10 54 5 0.3 Accumulated amount of metal per 1 g ofdry cells [g] 0.18 0.91 0.043 10.9

EXPLANATIONS OF LETTERS OR NUMERALS

-   -   1 and 1′ device for metal recovery    -   2 storage unit    -   3 concentration unit    -   4 return unit    -   5 measurement unit    -   6 supply unit    -   10 reaction solution storage tank    -   10′ reaction tank    -   12 concentration tank    -   14 membrane module    -   16 recovery unit and    -   18 filtered water storage tank

1. A method for concentrating a metal in a metal ion-containingsolution, the method comprising the following (1) to (3): (1) reducing ametal ion into a metal fine particle and accumulating the metal fineparticle in a microorganism by allowing the microorganism and anelectron donor to act on a metal ion-containing solution and thusobtaining a solution that comprises the microorganism having the metalfine particle accumulated therein; (2) concentrating the solution thatcomprises the microorganism having the metal fine particle accumulatedtherein by a filtration membrane and thus obtaining a concentratedsolution; and (3) returning the concentrated solution to (1) above. 2.The method for metal concentration according to claim 1, wherein themetal ion is an ion of one or more elements selected from the groupconsisting of Au, Ag, Pt, Pd, Rh, Ir, Ru and Os.
 3. The method for metalconcentration according to claim 1, wherein a metal that is produced byreducing the metal ion coexists when the microorganism and the electrondonor act on a metal ion-containing solution in (1) above.
 4. The methodfor metal concentration according to claim 1, wherein the electron donoris an organic substance having from 1 to 7 carbon atoms.
 5. The methodfor metal concentration according to claim 1, wherein the electron donoris at least one or both of an aliphatic carboxylic acid having from 1 to3 carbon atoms and a salt thereof.
 6. The method for metal concentrationaccording to claim 1, wherein the electron donor is at least one or bothof formic acid and a salt thereof.
 7. The method for metal concentrationaccording to claim 1, wherein the microorganism is iron-reducingbacteria.
 8. The method for metal concentration according to claim 7,wherein the iron-reducing bacteria are bacteria belonging to the genusShewanella.
 9. The method for metal concentration according to claim 8,wherein the bacteria belonging to the genus Shewanella are Shewanellaalgae or Shewanella oneidensis.
 10. The method for metal concentrationaccording to claim 1, wherein an average pore size of the filtrationmembrane is from 0.01 to 1.0 μm.
 11. A method for recovering themicroorganism from the solution formed as a result of (1) in claim 1,the method comprising the following (4): (4) recovering the solution soas to have a cell concentration of 1.0×10¹⁷ cells/m³ or less.
 12. Amethod for metal recovery from a metal ion-containing solution, themethod comprising the following (1′) to (4′): (1′) accumulating a metalion in a microorganism by allowing the microorganism to act on a metalion-containing solution and thus to obtain a solution that contains amicroorganism having the metal ion accumulated therein; (2′)concentrating the solution that comprising the microorganism having themetal ion accumulated therein by a filtration membrane and thus toobtain a concentrated solution; (3′) returning the concentrated solutionto (1′) above; and (4′) recovering the solution that contains themicroorganism having a metal fine particle accumulated therein so as tohave a cell concentration of 1.0×10¹⁷ cells/m³ or less.
 13. The methodfor metal recovery according to claim 12, wherein the metal ion is anion of one or more elements selected from the group consisting of Ga,In, Zn, Sn and a lanthanoid.
 14. The method for metal recovery accordingto claim 12, wherein the microorganism is iron-reducing bacteria. 15.The method for metal recovery according to claim 14, wherein theiron-reducing bacteria are bacteria belonging to the genus Shewanella.16. The method for metal recovery according to claim 15, wherein thebacteria belonging to the genus Shewanella are Shewanella algae orShewanella oneidensis.
 17. The method for metal recovery according toclaim 12, wherein an average pore size of the filtration membrane isfrom 0.01 to 1.0 μm.
 18. A device for metal concentration, comprisingthe following (a) to (c): (a) a storage unit to store a solution that isobtained by allowing a microorganism and an electron donor to act on ametal ion-containing solution so as to reduce a metal ion into a metalfine particle and also to accumulate the metal fine particle in themicroorganism or by allowing the microorganism to act on a metalion-containing solution so as to accumulate a metal ion in themicroorganism and contains a microorganism having a metal fine particleor a metal ion accumulated therein; (b) a concentration unit toconcentrate the solution that is transferred from the storage unit andcontains the microorganism having a metal fine particle or a metal ionaccumulated therein by a filtration membrane; and (c) a return unit toreturn a concentrated solution that is concentrated in the concentrationunit to the storage unit.
 19. The device for metal concentrationaccording to claim 18, the device further comprising the following (e):(e) a measurement unit to measure a cell concentration of the solutionthat is supplied to the concentration unit and contains themicroorganism having a metal fine particle or a metal ion accumulatedtherein.
 20. A device for metal recovery, comprising the following (a)to (d): (a) a storage unit to store a solution that is obtained byallowing a microorganism and an electron donor to act on a metalion-containing solution so as to reduce a metal ion into a metal fineparticle and also to accumulate the metal fine particle in themicroorganism or by allowing the microorganism to act on a metalion-containing solution so as to accumulate the metal ion in themicroorganism and contains a microorganism having a metal fine particleor the metal ion accumulated therein; (b) a concentration unit toconcentrate the solution that is transferred from the storage unit andcontains the microorganism having a metal fine particle or a metal ionaccumulated therein by a filtration membrane; (c) a return unit toreturn a concentrated solution that is concentrated in the concentrationunit to the storage unit; and (d) a recovery unit to recover thesolution that contains the microorganism having a metal fine particle ora metal ion accumulated therein from at least one or both of the storageunit and the concentration unit.
 21. The device for metal recoveryaccording to claim 20, the device further comprising the following (e):(e) a measurement unit to measure a cell concentration of the solutionthat is supplied to the concentration unit and contains a microorganismhaving a metal fine particle or a metal ion accumulated therein.